Electrode section-connecting nipple pre-assembly and process of assembling an electrode joint



June 1970 J. T. SNYDER ETAL 3,517,954

ELECTRODE SECTION-CONNECTING NIPPLE PRE1ASSEMBLY AND PROCESS OFASSEMBLING AN ELECTRODE JOINT Filed 001;. 23, 1967 United States PatentELECTRODE SECTION-CONNECTING NIPPLE PRE- ASSEMBLY AND PROCESS OFASSEMBLING AN ELECTRODE JOINT Joseph T. Snyder, West Nyack, N.Y.,Charles C. Maxfield, Chippawa, Ontario, Canada, and Francis H. Skinnerand James A. Whitwell, Lockport, N.Y., assignors to Great Lakes CarbonCorporation, New York, N.Y., a corporation of Delaware Filed Oct. 23,1967, Ser. No. 677,366 Int. Cl. E04g 7/00 U.S. Cl. 287127 7 ClaimsABSTRACT OF THE DISCLOSURE An electrode section-connecting nipplepre-assembly is made. The pre-assembly is used in assembling anelectrode joint which comprises the pre-assembly and another electrodesection. The pre-assembly is made prior to shipment to the user of thejoint. It is made in such a manner as to provide a clearance between thenon-load bearing flanks of the threads of the connecting nipple and thethreads of the socket of the electrode section of the preassembly. Also,prior to shipment of the pre-assembly to the user of the joint, a meansis employed to maintain the connecting nipple in a fixed position in thesocket of the electrode section of the pre-assembly thereby insuringthat the connection of the pre-assembly will not become loose duringshipment and thereby also maintaining the aforesaid thread clearance.After the pre-assembly is shipped to the user and is connected to theother electrode section of the final joint assembly, to complete themaking of the electrode joint, there is substantially even distributionof clearance between the threads of the nipple and the threads of bothelectrode sections of the final joint.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to the field of graphite or other carbon electrodes for electricfurnaces and like equipment, wherein the electrodes are consumed in useand wherein the electrodes must be continually fed into the furnace orother equipment where they are used. It particularly relates toelectrode joints that comprise a double-frusto-conical threadedconnecting nipple of electrode material whose two frusto-conicallytapering portions are in threaded engagement with respectivefrustoconical cup-shaped socket recesses in the butt faces of thecoaxially aligned electrodes and to the manner in which such a joint isassembled. However, the threaded nipples and their corresponding socketsor bore holes in the electrode sections may also have threaded sideswhich are parallel to the nipple axis. Such joints serve to add a newelectrode to the end of a nearly consumed electrode to permit acontinuous furnace operation by replenishing the electrode material inaccordance wtih the rate of consumption.

In making such joints, one end of the nipple is screwed into place in acorresponding bore or socket of one of the electrodes to the approximatemiddle of the nipple and then the other electrode section is threaded tothe other end of the nipple until the faces of the electrode sectionsare in contact. With a tapered nipple, its largest diameter is at itsmiddle and is also at the plane of contact between the electrodesections. The threaded depth of the nipples is generally the samewhether measured at the ends of the nipple or at its center and this istrue whether the nipple is straight or tapered. It is also usual, witheither type of connecting nipple, that in the assembled ice joint eachthread will possess a loaded flank, which is nearer the geometric centerof the nipple, and a non-load bearing or idle flank which is opposite tothe loaded flank. (That is, the idle flank is the flank nearer the endsof the nipple and the loaded flank is the flank nearer the geometriccenter of the nipple, and this is how these flanks are defined in thepresent invention.) The loaded flank generally carries most, if not all,of the compressive stress between the nipple and the electrode sections.

In this type of joint, the half that is assembled first usually containslittle or no clearance at the idle flank while maximum clearance occursat the idle flank of the second half assembled.

Such electrode joints are generally mechanically weaker than thefull-bodied portions of the electrodes. The joints are thereforeparticularly susceptible to breaking and are also subjected toadditional stresses by thermal tensions occurring during heating and/orcooling and shrinking of the electrodes. The high current loading ofmodern electro-furnaces causes additional stresses by overheating in thenipple portion at the junction places between the nipple and theelectrode sockets. All such thermal stresses are particularly criticalwith electrodes of large diameters, and in electric furnaces operatingat very high voltages as are used for reducing the meltingin period andincreasing the furnace capacity.

Description of the prior art The art has Well recognized theaforedescribed inherent mechanical weaknesses of electrode joints andthe stresses and thermal tensions to which they are subjected and hastaken or suggested several steps or procedures for minimizing same. As apart of the joint problem, the art has also recognized the adverseconsequences of improper or asymmetrical screwing-in of the connectingnipple into the sockets of the electrode sections joined by same, andhas suggested various expedients for minimizing or overcoming thisproblem. U.S. Pats. 2,957,716; 2,970,854; 3,088,762; 3,134,616 and3,140,967 and German Pats. 1,091,253 and 1,100,838 are all, for example,very pertinent to the problem of equal flank spacing or evenlydistributed thread clearance in electrode joints and to ways ofproviding same.

However, these patents and any other prior art references presentlyknown have all approached or attacked the problem of providing evendistribution of thread clearance from the point of view of trying tocompletely solve the problem at the place or site at which the joint isactually used and none have considered or suggested the possibility thata good part of the problem might be solved or overcome if part of themaking of the final joint were carried out or accomplished elsewherethan at the users site, such as at the site of the manufacturer of theelectrode sections and the nipple. The present invention is addressed toand based upon the taking of this latter approach to the solving ofelectrode joint problems and especially the problem of even distributionof thread clearance in electrode joints.

SUMMARY OF THE INVENTION An electrode section-connecting nipplepre-assembly is made. The pre-assembly is used in assembling anelectrode joint which comprises the pre-assembly and another electrodesection. The pre-assembly is made prior to shipment to the user of thejoint. It is made in such a manner as to provide a clearance between theidle or non-load bearing flanks of the threads of the connecting nippleand the threads of the electrode section of the preassembly through theuse of a temporary positioning means which is also used to coaxiallyposition the nipple in the electrode section. Also, prior to shipment ofthe pre-assembly to the user of the joint, a means distinct from thetemporary positioning means is employed to maintain the connectingnipple in a fixed position in the socket of the electrode section of thepre-assembly, after removal of the temporary positioning means therebyinsuring that the connection of the pro-assembly will not become looseduring shipment and thereby also maintaining the aforesaid threadclearance. After the preassembly is shipped to the user and is connectedto the other electrode section of. the final joint assembly, to completethe making of the electrode joint, there is substantially evendistribution of clearance between the threads of the nipple and thethreads of both electrode sections of the final joint.

Following are some of the features or benefits and advantages which canbe attained by proceeding in accordance with the present invention andby making or employing a nipple-electrode section pre-assembly in amanner such as just described:

(1) The connecting nipple can be centered or floated in one of theelectrode sections in the plant of the manufacturen That is, it can bemade in such a manner as to provide a clearance between the non-loadbearing flanks of the threads of the connecting nipple and the threadsof the socket of the electrode section of the pre-assembly. The nippleremains in this assembled form in the electrode section with theaforedescribed thread clearance and the pre-assembly is shipped to thecustomer. The possibility of the condition of the assembled form beingchanged or of the nipple becoming loose in transit or when thepre-assembly is connected to the electrode train of the furnace iseliminated by using a paste or cement or a locking substance or someother means as part of the pre-assembly to maintain the nipple in thefixed floating, centered position in the socket of the electrode withthe aforedescribed thread clearance. A primary advantage of proceedingin this manner is that the assembling of an improved electrode joint ismade more reproducible as compared to prior art techniques because avital part of its total assembly is carried out under closely controlledconditions rather than by those at the plant of the user of the jointwho may not appreciate the problems involved in centering the nipple andthe disadvantages which can result if the nipple is not properlycentered.

(2) Because of conditions at the site of where the joint is used, it isvery difiicult to make a good joint in which the nipple is properlycentered at such site. Usually the customer or user of the electrodesections and connecting nipples makes a non-floating pre-assembly at theplant so as to have it ready in case of breakage or major butt losses,etc., in the electrode train of the furnace, such often occurring dailyin some steel furnace plants. The said non-floating pre-assembly doesnot provide the optimum positioning of the nipple as described hereinand it may also be on the floor for any length of time, even a day orlonger during which time it is typically unprotected. Dust or particescan collect on or in the threads of the pre-assembly, and the threads orfaces of same can also be bumped or damaged, etc., because of theexposed conditions of the pre-assembly. Foreign objects on the threadsof the joint, or damaged threads, are, of course, very detrimental tothe making of optimum joints and/ or to optimum joint performance. Inthe case of the present invention, a floating pre-assembly has alreadybeen made for the customer and the end protectors, which are referred tohereinafter, can be left on until the last minute because they can beremoved very quickly. In other Words, there is no longer any concern onthe part of the customer of the time required to take nipples andelectrode sections out of separate boxes or crates and to make apre-assembly as there is under the usual former practices. Under formerpractices, this time element is also, of course, of great concernbecause it can cause furnace down-time and consequent production lossesand this is the reason why the customer typically made one or morepre-assemblies in order to try to avoid or minimize such furnacedown-time.

(3) Pre-assembly at the plant of the manufacturer or prior to shipmentto the user more readily permits the selection of the proper class ortype of nipple to correpond with the electrode. The relative values ofthe coefficients of thermal expansion (CTEs) of the nipple and of theelectrode sections connected by the nipple are very important for properor optimum joint design and performance, but knowledge of these valuesis much more within the province of the manufacturer or supplier than itis to the user, who may be entirely unaware of these factors at the timehe makes the joint connections. The foregoing considerations apply also,but to a lesser degree, to such relative properties of the nipple andelectrode sections as strength and resistivity, which should also beintelligibly matched with a proper consideration of their values inorder to insure the making of optimum joints. The possibility,therefore, of the customer or the user of the joint using nipples whichdo not match well with the electrodes, or vice versa, is eliminated orreduced;

(4) The customer or user of the joint is provided with a labor-savinginasmuch as half of his customary assembling operation is eliminated andhe is not required to assemble a free nipple into one of the electrodes.Rather, the customer joins one nipple, electrode-section pre-assembly toanother such pro-assembly (which may already be on the furnace) or toanother electrode section, such as to the last electrode section of theelectrode train of the furnace. The cost-saving to the customer varies,therefore, depending on whether the customer made assemblies on thefloor or on the furnace. Regardless of which method he uses, theemployment of pre-assembly of the present invention provides alabor-savings.

An obvious danger of shipping an electrode-nipple preassembly is thepossibility of damage while in transit. This is overcome in the presentinvention by protecting the entire exposed machined threaded portion andend or face of the nipple (and typically also, the electrode sectionface as Well) with a suitable covering, such as molded polyurethanefoamed resin. The opposite socketed end of the electrode section of thepre-assembly, which is internally threaded, is also typically coveredsuch as with a standard type end protector, viz cardboard taped to theface.

BRIEF DESCRIPTION OF THE DRAWING It has been found that the foregoingadvantages or benefits are achievable by making a nipple-electrodesection pre-assembly as illustrated in vertical cross-section in theattached drawing and by using such a pro-assembly as part of each jointassembly used in the electrode train. The drawing also illustratesauxiliary equipment or temporary positioning means, viz a centering jig,which may be used in carrying out the process or in making thepreassembly of the present invention.

DETAILED DESCRIPTION OF THE DRAWING AND THE PREFERRED EMBODIMENTS In theembodiment illustrated in the drawing, a centering jig is employed inorder to apply an independent axial or longitudinal pressure or forceupon the nipple and in order to provide a clearance at the idle flanksof the threads of the nipple and the opposing internal threads of theelectrode section into which the nipple is threaded.

Nipple 1, which as previously stated is preferably tapered, waspre-heated to C. and was then threaded into a correspondingly threadedsocket of electrode section 2. The nipple had a one-third pitch, i.e.three threads per inch, and a taper of 1 to 6, i.e. its radius decreasedby one inch for every 6 inches of length of the nipple away from themaximum diameter. The nipple was threaded into the socket until itsmajor diameter, indicated generally at 3, coincided approximately withthe plane of the face 4 of the electrode section and until it washandtight, i.e. until the threads of both the nipple and electrodesocket section were completely engaged. In the illustrated embodiment,the nipple was provided with a lengthwise (longitudinal) hole 8 betweenits ends 6 and 9. Also in this embodiment, the nipple had a majordiameter of the diameter of the longitudinal hole was 1%" and thediameter of the electrode section was The aforementioned centering jigconsists of an internally threaded plate 18 (2 inches thick) which wasthreaded onto the free end of the nipple. Casters 19, were coupledthrough holes in the centering plate to 1 /2" diameter bore aircylinders 17, and contacted the face 4 of the electrode section 2. Threecasters and three air cylinders were used, the casters being so spacedas to form an equilateral triangle against the face 4 of the electrodesection 2. A source of air (not shown) provided air under pressure (200psi. each) to the air cylinders. The arrangement was such that thecasters 19 pushed in one direction against the face 4 of the electrodesection while the threaded plate 18 pulled the nipple 1 in the oppositedirection, thus applying an axial pressure or force upon the nipple.While this axial force was still being applied, the nipple was backedoff a slight amount (e.g. 45) thus providing a clearance 12 between theidle flanks 13 of the threads of the nipple and the opposing flanks ofthe threads of the socket of the electrode section 2 and thusprepositioning the nipple in the socket of the electrode section. Thisaxial pressure also caused the load-bearing flanks 11 of the threads ofthe nipple (viz the flanks nearer the geometric center of the nipple) toremain in direct and close contact with the mating threads of theelectrode socket. A two-component polyurethane foaming material was thenmixed for about 20 seconds and a measured amount of same was injectedthrough the lengthwise or longitudinal hole 8 and into the cavity orspace 5 between the base 6 of the nipple and the base or bottom 7 of theelectrode section socket. A sufiicient amount of the foaming materialwas employed so as to substantially fill the space 5 and extend well upinto the longitudinal bore 8 after foaming and becoming rigid. Thenipple-electrode section assembly was in a horizontal position when thiswas done and the electrode was then rolled 180 in order to assist thefoaming material in substantially filling this space, after foaming.The-assembly was maintained in a fixed position for approximately 10minutes, to allow the foaming material to expand, set and become rigid,after which the pressure was released and the jig removed. The specific(floating) positionof the nipple in the electrode section socket,previously provided by the centering jig, was maintained by the settingand expansion of the foaming material.

When such a nipple-electrode section pre-assembly as just described isadded to a second electrode section of an electric furnace electrodecolumn or train, the nipple in the resulting 3-membered joint (viz twoelectrode sections with the nipple half-threaded into each) will be solocated that there will be a substantially even distribution ofclearance between the idle flanks of the threads of both halves of thenipple in the electrode section sockets of the final joint assembly,rather than the common and objectionable condition typically encounteredin the prior art of no clearance at the idle flank of the threads of thenipple-half first assembled and maximum clearance at the idle flank ofthe threads of the second nipple-half assembled. Stated in another way,the assembling of an improved electrode joint is made more reproducibleas compared to prior art techniques wherein the entire assemblyoperation is carried out at the plant of the user.

The backing-off of 45 of the nipple in the embodiment just described issatisfactory for a nipple having a pitch and taper as set forth. In amore general sense, the

number of degrees backed-off will depend on the pitch and taper of thenipple because the clearance between the threads is a function of thesetwo variables. For standard nipples having a one-third pitch and a taperof 1 to 6, the number of degrees backed off will typically be a valuefrom about 45 to about for standard nipples having a one-fourth pitch (4threads per inch) and a taper of 1 to 6, the number of degrees backedoff will typically be a value from about 60 to about There are severalmaterials which expand upon solidification and which may be used in thespace 5 between the base of the nipple and the base of the electrodesection socket in the present invention in order to help float thenipple in the socket of the electrode section and in order to maintainthe nipple in a fixed position in the electrode socket. Such materialsinclude foaming resins which expand and become rigid upon foaming. Mostof these are made by mixing the foamable material with a catalyst and/or foaming agent just before introducing or injecting the mixture intothe aforesaid space. Such foamable resin materials which become rigidupon setting include polyurethane, polystyrene and polyvinyl chlorideresin formulations well known to those skilled in the art of makingrigid plastic foams.

Several molten metal alloys also have the property of expansion uponsolidification and may be used in the space 5 in the present inventionin order to maintain the desired clearance between the threads and inorder to maintain the nipple in a fixed position in the electrodesocket. (As the metal solidifies and expands, the nipple 1 is kept orlocked in the desired position in the socket of the electrode.) Thefollowing compositions, wherein the numbers are approximate percentagesby weight, and having the properties set forth opposite same, aretypical or preferred alloys which may be used:

Properties Melting temperature or range Electrical resistivity of alloyin ohm-inches 0. 82X 10 5 O. 49X 10- Alloy copper (e) 15 antimony, 82lead, 3 tin 275 Because of the fact that all of the foregoing alloysexhibit a cumulative growth during and after solidification (as a resultof expansion either upon being cooled from their molten state to theirsolid state, and/or because of linear growth after solidification), avery tight connection is made between the nipple and the electrodesection. The connection so made is also very strong mechanically and hasa very low electrical resistance.when any of these alloys is used inmaking the pre-assemblies or joints as described herein.

The present invention is intended to include any nippleelectrode sectionpre-assembly made prior to shipment to the user wherein the pre-assemblyis made in such a manner that a temporary positioning means is employedto provide a clearance between the idle or nonload bearing flanks of thethreads of the connecting nipple and the threads of the socket of theelectrode section of the preassembly, and wherein, prior to shipment ofthe pre-assembly to the user, a means distinct from the temporaryposition means is employed to fixedly maintain the connecting nipple inthe position in the socket of the electrode section of the pre-assemblyinitially provided by the temporaty position means, thereby alsomaintaining the aforesaid thread clearance after the temporary positionmeans has been removed. Although the foregoing described techniques(referred to in connection with the drawing) for accomplishing theseconditions are preferred, it should be appreciated that there areseveral other ways also of carrying out the invention. For example, thepre-assembly does not have to be made using a nipple containing alengthwise hole and an expandable material injected or introducedthrough said hole. Rather, the nipple may be solid but floated in theelectrode section socket by using a centering jig to hold it temporarilyin place as described and it may then be fixed permanently in place inseveral ways such as by providing or drilling one or more transverseholes in the electrode section socket wall and injecting a cement orpaste or binder in said holes and heating said materials until they setso as to lock the nipple in place. (Preferably such hole or holes wouldlead to the space between the base of the nipple and the bottom of theelectrode socket, but it or they may also lead to the threaded areabetween the nipple and the socket.) Or locking pins may be inserted ordriven through such radial holes so as to exert a mechanical lockingaction (rather than a cementing action) against the nipple, so as tomaintain the nipple in a fixed position in the electrode socket of thepre-assembly, with the idle flanks of the threads of the nipple floatingin the electrode socket. Or a lengthwise hole may be used in the nipple,together with a centering jig to hold the nipple temporarily in place,and a filling substance may then be injected through the hole to fillthe space between the base of the nipple and the bottom of the electrodesocket. The filling substance need not be expandable, just so long asenough of it is in jected into the space while the axial force is stillbeing applied by the centering jig, so that when the centering jig isremoved, the idle flanks of the threads of the nipple are prevented fromfalling or moving and thus contacting the mating flanks of the threadsof the socket.

In other words, the main novel aspects of the present invention do notreside in the particular means which are employed to maintain the nipplefixed in the electrode socket, with a clearance between the non-loadbearing flanks of the threads of the nipple and the threads of thesocket, but rather reside in the broader concepts of providing apre-assembly, of preparing this pre-assembly in a prescribed manner soas to have the aforedescribed thread clearance prior to shipping it tothe user of same, and in insuring, prior to shipment of the pre-assemblyto the user, that the user receives same in the same ideal conditionthat it was when-it was shipped (no matter what particular means areemployed to maintain the nipple in this condition). By so following orcarrying out these concepts, the aforediscussed several advantages ofthe present invention over the prior art practices are thus realizablewhen the pre-assembly is then shipped to its user and is then added toanother internally threaded electrode section to complete the making ofthe electrode joint.

It is to be understood that the invention is not limited to the specificdetails which have been offered merely for illustrative purposes andthat modifications may be made Within the scope of the appended claimswithout departing from the spirit of the invention.

I claim:

1. A process of producing a ready for shipment electrode section-nipplepre-assembly, for use in an electrode joint comprised of saidpre-assembly and a second electrode section, said nipple being threadedand said sections possessing correspondingly threaded internal socketsextending inwardly from their end faces, which comprises:

(a) threading one end of a threaded nipple into the internally threadedsocket of an electrode section in such a manner as to coaxially positionthe nipple in said electrode section socket by a temporary posi- 8tioning means and also in such a manner that the temporary positioningmeans provides a clearance between the non-load bearing flanks of thethreads of said nipple and of said threaded electrode socket, the otherend of said threaded nipple projecting outwardly from said socket;

(b) employing a means distinct from the temporary positioning means tofixedly maintain the nipple in the position in the electrode socketprovided by step (a) with the coaxial positioning and the threadclearance preserved; and

(c) removing said temporary positioning means from said nipple fixedlypre-positioned in the electrode section;

said pre-assembly being adapted to be added to a second electrodesection to complete the making of the electrode joint by threading theprojecting end of the nipple into said second electrode section therebyalso providing substantially even distribution of clearance between thethreads of said nipple and the threads of the sockets of the electrodesections in the making of the final joint assembly.

2. A ready for shipment electrode section-nipple preassembly madeaccording to the process of claim 1.

3. A ready for shipment electrode section-nipple preassembly madeaccording to the process of claim 1 wherein the projecting threadedportion and the face of the nipple on one end of the pre-assembly areprotected with a covering before the pre-assembly is shipped to itsplace of use.

4. A pre-assembly made according to the process of claim 1 wherein thethreaded socket of the electrode section and the nipple threaded intosaid socket are correspondingly tapered.

5. In the process of assembling an electrode joint comprising twoelectrode sections containing internally threaded sockets which extendinwardly from end faces of said sections and a threaded nippleconnecting said sections by being threaded into said sockets, theimprovement wherein the joint is made utilizing the preassembly of claim1.

6. A process of assembling an electrode joint according to the processof claim 5 wherein the projecting threaded portion and the face of thenipple on one end of the pre-assembly are protected with a coveringbefore the pre-assembly is shipped to its place of use and wherein thecovering is removed before the preassembly is added to the otherelectrode section of the joint.

7. A process of assembling an electrode joint according to the processof claim 5 wherein the threaded sockets of the electrode sections aretapered and wherein the nipple threaded into said sockets are taperedand wherein the nipple threaded into said sockets is correspondinglytapered.

References Cited UNITED STATES PATENTS 3,140,967 7/1964 Kaufmann et al.287-127 X 2,873,765 2/ 1959 Gregory 138-96 2,957,716 10/1960 Kaufmann etal.

2,989,087 6/ 1961 Higgins 138-96 3,088,762 5/1963 Kaufmann et al.

3,134,616 5/ 1964 Kaufmann.

DAVID J. WILLIAMOWSKY, Primary Examiner W. L. SHEDD, Assistant ExaminerUS. Cl. X.R.

